The number of knee prostheses implanted every year is increasing regularly, evidence of the growing confidence inthis type of implant and the increasing number of implants inyoung patients. This is why the choice of a prosthesis is nolonger simply made on the basis of analgesic treatment, butalso on the best possible functional solution. Patients are nolonger satisfied to be simply pain free, but want to walk, godown stairs easily, enjoy leisure activities (gardening, cycling,swimming, etc.) or more, under the best conditions. Completeor almost complete flexion is required. This is why the old nonanatomicalcam implants have shown their limits and surgeonsnow opt for implants which optimise mobility, joint kinematicsand patella movement.
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Within this context, the 3DKnee prosthesis distributed by Lima Corporate provides function based on tibiofemoral stability
around a lateral pivot while preserving the tried and tested principles of a sliding prosthesis. Based on the principle that the anterior cruciate ligament must be sacrificed for any knee prosthesis, it has been designed to limit the anterior instability engendered. Its asymmetrical condyle design provides extensive sliding owing to the wider, longer internal condyle, which is closer to the natural roll-back movement. A posterolateral lip, combined with a shorter external condyle limits external sliding and reinforces stability: this is the lateral pivot principle. This choice requires anatomical asymmetrical tibial plates. The lateral congruence increased by the posterior lip is intended to reduce occasional biomechanical stress, while providing a point of stability in flexion movements. Does this generate a greater risk of wear? work published with 4 years follow-up and studies on simulators (5 million cycles) are reassuring on this subject. Using tried and tested high molecular weight polyethylene combined with wider tibiofemoral contact zones and extended preservation of “natural” mobility are factors which limit wear. Finally, the patello-femoral design improves patella movement at the cost of deeper hollowing of the femur in the subtrochlear region, enabling high quality patellar resurfacing; patella stability is guaranteed.
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Because of its anatomical design, this prosthesis requires accurate positioning and optimal ligament balancing; the broad release of the internal tibial plate allows the sliding movement to take place and ensures symmetrical balance in flexion-extension, without locking the lateral compartment. This ligament balancing takes place in flexion first then in extension; theoretically there is not much bone cutting to be done and it is the gradual release of ligament tension which leads to good balancing of the implant. Clinically, the lack of a cam generates a moderate posterior drawer during flexion but this has no effect on walking or going downstairs. Mobility is at least equal to that of a “classic” total knee prosthesis, but is still dependent on preoperative amplitudes. Patella stability is good and is governed by the absence of pain in the patello-femoral system.
In conclusion, the 3DKnee prosthesis distributed by Lima Corporate is an interesting development in sliding prostheses because it targets a physiological movement, without preserving the cruciate ligaments but with accurate peripheral balancing. The results published by the designers of this implant and the first clinical results, support this concept.
|André Ferreira
|Clinique du Parc
|Lyon - France
